A semiconductor wafer (a type of disc wafer) is treated through a film forming process or etching process to for example concentrically form an insulating film, conductive film, or other processing region on the surface. In the past, the technique of determining whether the edge of the processing region (insulating film etc.) formed on this semiconductor wafer is in a properly finished state without curling etc. has been proposed (see Patent Document 1). This technique captures images of a plurality of locations of the outer edge of the semiconductor wafer and measures from the captured images the exposed width between the outer edge and the edge of the processing region at the plurality of locations of the semiconductor wafer so as to determine from the state of the exposed width at the plurality of locations whether the edge of the processing region (insulating film etc.) is in a proper finished state with no curling etc.    Patent Document 1: Japanese Patent Publication (A) No. 2002-134575